1. Field of the Invention
The present invention relates generally to cable television distribution networks. More particularly, the present invention relates to a node in a HFC infrastructure-based CATV network utilized as an advanced interfacing device between the fiber optic segment and the coaxial segment of the CATV infrastructure.
2. Discussion of the Related Art
In CATV distribution networks based on a Hybrid Fiber Coax (HFC) plant infrastructure the fiber optic trunk and the coaxial trunk of the network are connected via specific devices typically referred to as fiber nodes. In the downstream the fiber node receives optical signals from the head-end via fiber optic cables, converting the optical signals to an RF signal and feeding the RF signal to the network subscribers via the coaxial portion which typically includes the distribution and drop cables and associated amplifiers and splitters. In the upstream the fiber node receives an RF signal from subscribers via the coaxial portion of the network, converts the RF signal to optical signals and feeds the optical signals via the fiber optic portion of the network back to the head-end.
Presently signals transmitted across a standard cable television infrastructure, from a head-end to a network subscriber and back from the network subscriber to the head-end, are modulated such as to have a bandwidth with a frequency range of about 5 MHz to about 860 MHz. The signals carry diverse encoded information units representing content, services and applications. Logically related and physically grouped information units are suitably modulated into distinct specifically allocated transmission channels. The channels are distributed across the available frequency range according to a predefined frequency plan. The number of potentially available downstream channels from the head-end to the subscriber and upstream channels from the subscriber to the head-end for the subscribers depends directly on the available bandwidth of the signal. The currently utilized signal with an about 5 to 860 MHz transmission bandwidth limits the number of available downstream and upstream channels. In many applications the 5-42 MHz portion of the signal is used for upstream transmission and the 50-860 MHz portion of the signal is used for the downstream or forward portion.
The Data Over Cable Services Interface Specification (DOCSIS) protocol has proven itself a successful product for broadband Internet access to the residential subscribers. Some Multi-system Operators (MSOs) are beginning to provide DOCSIS to small and medium businesses as a best effort connection for Internet access. However, DOCSIS over existing HFC networks can not be used as an alternative to existing high-speed data services as the existing HFC networks do not have the transmission spectrum to carry the high speed data for the small and medium businesses (SMB), which require substantial data throughput in the upstream as well as in the downstream direction. The transmission spectrum problem is particularly acute in the upstream where out of the about 15 to 42 MHz portion of the signal used less than 20 MHz are usable. In addition, equipment which is based on the DOCSIS standard, such as the so-called CMTS routers, located in the head-end of the HFC networks is now suitable for broadcast and reception of a signal ranging between about 5-860 MHz.
The current solution for increasing the upstream capacity, which is referred to as node splitting, involves costly investment as well as only 80 MHz of the 100 MHz available since some of the spectrum is dedicated to common service for all nodes. The co-pending related PCT patent application PCT/IL00/00655 describes and teaches a system and method of a CATV network having a bandwidth of about 5 to about 3000 MHz for the transmission of upstream and downstream wideband signals within. The CATV network could be a standard coaxial media-based plant or an HFC-infrastructure. The system and method proposed by the above-mentioned related patent application involves the installation and/or modification of a set of active and passive components along the signal transport path of the network in order to enable the transmission of a wideband signal with a frequency range of about 5 to 3000 MHz and higher.
It is however desirable to continue use of the equipment presently operative in the head-end of the CATV network, such as but not limited to DOCSIS CMTS routers, while providing a bandwidth in excess of 860 MHz. It is also desirable to make use of the DOCSIS protocol for transfer of data in the upstream direction employing multiple upstream bands without making substantial investment in upstream physical node splitting thus providing networking services to subscribers, small and medium-sized businesses.